NATURAL PHILOSOPHY. ] 43 



the existence, on an average, of one soldier in every fifty- five unable 

 to distinguish a scarlet coat from green grass would not issue in 

 grave inconvenience, and ere this have forced itself into prominence 

 by producing mischief. Among the circle of my own personal 

 acquaintance I have only known two (though, of course, I have 

 heard of and been placed in correspondence with several) ; and a 

 neighbour of mine, who takes great delight in horticulture, and 

 has a superb collection of exotic flowers, informs me that among 

 the multitude of persons who have seen and admired it, he does not 

 recollect having ever met with one who appeared incapable of appre- 

 ciating the variety and richness of the tints, or insensible to the 

 brilliancy of the numerous shades of red and scarlet. It may be, 

 however, that the percentage is on the increase — certainly we hear 

 of more cases than formerly ; but this probably arises from the fact 

 of this, like many other subjects, being made more generally matter 

 of conversation." — Proceedings of the Royal Society. 



THE DICHROO SCOPE. 



This apparatus, the invention of Prof. Dove, and described in 

 PoggendorfT's Annalen, is intended for the following purposes : — 



1. To represent interferences, and spectra in different-coloured 

 lights, both separately and combined. 



2. To imitate the phenomena of dichroism both in the case in 

 which the dichroitic crystals are viewed through a double-refracting 

 arrangement, as, for example, Haidinger's dichroitic lens ; and also 

 in the case of the phenomena produced when the dichroitic crystals- 

 themselves are used as analysers in a polarizing arrangement. 



3. To combine elliptically, circularly, and rectilinearly polarized. 

 and unpolarized light, not in such a manner that the one is produced 

 by the polarizing, and the other by the analysing arrangement, bul; 

 80 that they traverse the doubly refracting media simultaneously, 

 and are then submitted to an analysing arrangement. 



(For details, see the entire paper, translated in No. 134 of the 

 Philosopliival Magazine.) 



THE CHROMOSCOPE. 

 Mr. J. B. Perth has sent to the British Association a specimen 

 of the cut-out card by the rotation of which over a black ground in 

 strong light, as sunlight, he could produce rings of various colours. 

 There were also diagrams exhibited, painted so as to represent the 

 several colours and tints of which the author had succeeded in 

 causing the rings to appear. This communication gave rise to much 

 conversation in the Section. Prof. Stevelly stated that Yir. Patter- 

 son, of Belfast, had commissioned him to mention at the first meet- 

 ing of the British Association which he had the honour of being 

 present at (Edinburgh, 1834), as an unexplained fact, that walking 

 rapidly past high iron railings, while the country on the other side 

 was covered with snow, and the sun shining brightly, the whole 

 landscape suddenly assumed a reddish or crimson hue. His atten- 

 tion being thus arrested, he found that, by altering the speed at 



